Definition 3 ([1]}) 
The agents \(\lbrace a_i,a_j\rbrace \)  form a blocking pair if (i) each of \(a_i\)  and \(a_j\)  find one another acceptable; (ii) either \(a_i\)  is unmatched or prefers \(a_j\)  to her partner in \(M\) ; and (iii) either \(a_j\)  is unmatched or prefers \(a_i\)  to her partner in \(M\) .

